1. Field of the Invention
The present invention relates to oscillatory wave motors.
2. Description of the Related Art
In recent years, oscillatory wave motors have been commercially used as, for example, motors for driving auto-focus lenses of single-lens reflex cameras, because of their low-speed and large-torque characteristics. Such oscillatory wave motors are required to have a smaller size and a larger output.
In order to reduce the size while increasing the output, measures must be taken against heat generation and temperature rise of oscillatory wave motors.
That is, the energy loss, which is the energy inputted into an oscillatory wave motor but not outputted therefrom, is converted into thermal energy.
Therefore, if an oscillatory wave motor is reduced in size while increased in output, the energy loss per unit volume and the energy loss per unit surface area increase, causing temperature rise.
Such temperature rise degrades the function of components of the oscillatory wave motor and affects the performance of the oscillatory wave motor. Accordingly, measures must be taken against such a problem.
To counter this problem, Japanese Patent Laid-Open No. 3-253270 proposes an oscillatory wave motor having an increased heat dissipation efficiency, as shown in FIG. 4.
As shown in FIG. 4, this oscillatory wave motor is configured such that a piezoelectric element 104 is bonded to one side of a ring-like metallic elastic member 103 and such that alternating voltages having different phases are applied to two driving piezoelectric element groups formed on the piezoelectric element 104.
By applying the alternating voltages, two standing waves are excited on the elastic member 103. By combining these standing waves, a traveling wave, which is a bending vibration, is formed. A ring-like moving-body main ring portion 106, to which an abrasion-resistant member 107 is bonded, is pressed against the other side of the elastic member 103 by means of a pressure spring 110. The moving-body main ring portion 106 and the abrasion-resistant member 107 constitute a moving body 108. The moving body 108 and an output shaft 111 are rotated by the friction drive produced by the traveling wave formed on the elastic member 103.
Meanwhile, the above-described Japanese Patent Laid-Open No. 3-253270 takes the following measures to counter heat generation and temperature rise of the oscillatory wave motor. The frictional heat generated between the moving body 108 and an oscillator 105, which is composed of the elastic member 103 and the piezoelectric element 104, as well as the heat generated in the oscillator 105, heats the oscillator 105.
The heat is conducted from an inside-diameter portion of the oscillator 105, which is in contact with a base 102, through a heat-conducting member 116 to a cover 101 and is quickly dissipated by a fan 117.
However, this configuration requires a separately provided heat dissipating member, such as a fan, which increases the component count, making a reduction in size difficult.
Furthermore, in this configuration, the heat-conducting member 116 inhibits oscillation of the oscillator 105 and degrades the performance.
A configuration in which heat is dissipated outside without providing the fan 117 or the heat-conducting member 116, but by means of heat conduction of other members, causes the following problems. The heat generated by the friction between the elastic member 103 and the moving body 108, the heat generated in the piezoelectric element 104, the heat generated at the bonding surface between the elastic member 103 and the piezoelectric element 104, and the heat generated in the elastic member 103, at a portion near the piezoelectric element 104, are dissipated by heat conduction through an elastic-member thin portion 103-b serving as an oscillator supporting member.
Alternatively, the heat is dissipated from the moving body 108 side, by heat conduction through a rubber ring 109 serving as a damper, a pressure spring 110 serving as a pressure-applying member, and an output shaft 111.
However, the elastic-member thin portion 103-b, serving as the oscillator supporting member, has a small thickness so as not to inhibit oscillation of the oscillator 105, and thus, has a small cross-sectional area. This is not suitable for heat conduction.
Furthermore, the rubber ring 109 serving as a damper is made of a low heat-conducting material, and the pressure spring 110 has a small thickness so as to reduce the spring constant to ensure the precision of pressure setting. This also inhibits heat conduction.
In addition, components of the oscillatory wave motor are fastened with screws and the like, and thus, heat is conducted between different components through the contact surfaces therebetween. Thus, the thermal contact resistance prevents heat conduction.
As has been described above, conventional oscillatory wave motors cannot sufficiently dissipate heat. Thus, temperature rise of oscillatory wave motors degrades the function of the components thereof and degrades the motor performance.
The present invention has been made in view of the above-described problems, and it provides an oscillatory wave motor capable of preventing degradation of performance due to temperature rise and reducing the size while increasing the output.